This invention relates to a surface treatment apparatus for effecting a surface treatment of electrodes of an object such as a board and an electronic part, and also relates to a wire bonding apparatus for bonding an electrically-conductive wire to the electrode of the board surface treated by this surface treatment apparatus.
In view of the trend toward the small-size design of electronic equipment, attention has been directed to techniques mounting electronic parts on a board, having a circuit pattern, at a high density. In one such technique, a bare semiconductor chip is mounted or placed directly on the board, and then this semiconductor chip is electrically connected to electrodes of the board by thin, electrically-conductive wires (having a diameter of about 25 .mu.m). The semiconductor chip and the wires are then coated with a resin for sealing purposes.
In many cases, the wire used for this purpose is made of gold, and in view of the bonding with the gold wire, the electrodes of the board are plated with gold. The circuit pattern is usually made of copper, and since gold is not bonded directly to this copper, one or more layers of metal (called a barrier metal layer) are formed on the copper electrodes, and then the surface of this layer is plated with gold. Nickel is most frequently used as the barrier metal.
The thickness of the gold plating film has heretofore been thought to have a great influence on the bonding strength of the wire, and it has been believed that unless the gold plating film is as thick as about 0.3 .mu.m, the wire can not be bonded satisfactorily.
There are known an electroplating method and a reduction electroless plating method which are capable of forming a thick gold plating film. A problem associated with both methods, however, is that the cost is high since a plating process must be effected for a long period of time.
Therefore, the inventor of the present invention has previously earlier filed an application for a method in which a wire can be bonded with sufficient strength even if the thickness of a plating film is small (Japanese Patent Unexamined Publication No. 7-106363). Since in this technique, the wire can be bonded to a gold plating film having a thickness of as little as 0.05 .mu.m, the cost for the gold plating can be greatly reduced.
In this technique, (1) a nickel compound is removed from the surfaces of electrodes of a board by a surface treatment apparatus, and then (2) wires are bonded respectively to the electrodes by a wire bonding apparatus.
These steps are required to be carried out with a high efficiency so that the above cost reduction effect will not be affected. However, at present, there is no facility to achieve this requirement. Particularly, there exists no surface treatment apparatus which is compact in size, and which thus can be incorporated in a production line, therefore preventing the new process from extensive use. Therefore, the present invention has been made to provide the optimum system for this new process.